Miniature Piston Actuators can be used as electro-explosive devices (EEDs). Such devices have been used as part of an Electronic Thermal Battery Initiator (ETBI) to provide a mechanical output to initiate a thermal battery.
Thermal batteries are designed for immediate and short duration activation under extreme operating conditions. In an inert state suitable for storage, a thermal battery is dormant, and can remain inactive for long periods of time. Upon initiation, a thermal battery instantly activates to serve as an accurate, low-impedance, voltage source that is stable for a predetermined time duration.
Additionally, explosive and pyrotechnic devices such as explosive bolts, bolt cutters, separation fairings, actuators, engine igniters, etc., are used in aeronautical and aerospace applications to perform various functions such as the separation of one structure from another, the release of a structure from a stowed position to a deployed position, etc. They are also used in the safety systems of land vehicles such as automobiles, for the deployment of air bags. Such devices are typically coupled to electrically operated initiators which, in response to suitable electrical signals, initiate the devices.
In aeronautical and aerospace devices such as missiles, satellites, launch vehicles, etc., and in land vehicle safety systems, the initiators in the ordnance firing systems that control the various explosive or pyrotechnic effectors typically comprise a hot bridgewire initiating element and an initiating charge of explosive or pyrotechnic material which is sensitive to the initiating element. In order to stimulate the hot bridgewire initiating element to release sufficient energy to ignite the ignition charge, a large amount of electrical energy (relative to what is generally required for most other functions on such devices) is required. For example, the firing of a hot bridgewire initiator typically requires a draw of several (typically 2-3 or more) amps from a 28-volt source for a period of about 0.05 second. Since there may be numerous effectors on a given device, the total energy requirement for initiation of the effectors may exceed the energy requirement for operation of the circuitry that controls the device. For this reason, ordnance firing systems typically include a dedicated high power energy source such as a thermal or chemical battery, for the purpose of providing sufficient energy to fire the hot bridgewires. The need in aerospace and aeronautical devices to provide such batteries, which are large and heavy, has been viewed as an unavoidable but significant burden. The batteries occupy space which could go to other, more useful, components of the device or to increased payload capacity and for airborne devices. They also increase the fuel consumption of the device at all times during flight. In some applications, such as for initiation of a thermal battery of a munition after launch, this energy requirement is impractical. A miniature piston actuator (PA) with a very low firing energy requirement which can provide a mechanical output to initiate the thermal battery is thus needed.
The current generation of piston actuators (PAs) for applications utilizes potassium dinitro benzo furoxan (KDNBF) as the explosive charge material and platinum as the bridgewire. KDNBF charge material is used to maximize gas generation to provide the actuating force. These PAs have an appreciable failure rate (˜5%) especially at cold temperature (−40 C), even when they were provided a firing energy greater than the all-fire energy requirement.
Current piston actuators do not provide a sufficiently high reliability within the constraints of available volume and electrical firing energy. Such devices are limited in their operation in that they suffer from poor reliability, including under exposure to extreme acceleration, limited altitude operation range, and narrow temperature operation range-especially at low operating temperatures. Additionally, they should remain safe and not be susceptible to premature detonation.
In these environments, weight and volume are at a premium, and an increase in system weight and volume presents packaging and weight management problems which may require significant engineering time to solve.
What is needed, therefore, are more reliable actuators.